CCWN 75:43
CONVERSION OF THE HD-10 KEYER TO CCW Chas Woodson

          The Heath HD-10 keyer can be easily adapted to CCW by
converting the dot multivibrator from a free running
multivibrator to a flip flop multivibrator which operates only
when pulses from another source are present. Note the dash
generator is this kind of multivibrator so it can serve as a
model.            For my keyer, I added 50K resistors across C10
and C20. This can be done on the foil side of the printed circuit
board so the unit does not have to be removed from the case. The
speed and dot space controls can be disconnected by removing the
leads to their center wipers. A shielded cable, run through the
hole of the head phone jack, brings in 5 cycles from the standard
which is coupled by a .01 capacitor to drive the flip flop. These
modifications can easily be removed if one should wish to return
the keyer to its original mode.            The output is CCW with
dot length of .1 second. I have also run this keyer with 1 second
and 10 second dots and found it works although the coupling
capacitor must be increased.            Operation has been
checked by oscilloscope and on the air. I have made over 50
contacts using CCW transmission with this keyer and it seems to
work fine. Rarely, about once every four minutes of sending, I
have noticed that the first dot of a character appears to be
longer than it should be, perhaps 1.5 or 2 times. I don't know
why this occurs but it doesn't appear to be a major problem.      
     CCW keying is a bit different experience as you must key in
phase with the standard. I found after a few contacts I learned
to do so without difficulty and can now send several minutes
without a keying error, although I still occasionally make
errors. One can press the dot key and release it and have nothing
happen if the enable does not cross the start of a pulse period.
Apparently I have learned to hold the keyer in the selected
position for the first bit of a word until that bit starts. Once
it starts one sends in a manner similar to standard keying except
that you must keep in phase with the reference pulses but this is
easy to learn to do as you are hearing them from the keying
monitor.